Proteomics Provides Insight into the Interaction between Mulberry and Silkworm

Effects of Habitual Dietary Change on the Gut Microbiota and Health of Silkworms

Diet plays a crucial role in shaping the gut microbiota and overall health of animals. Traditionally, silkworms are fed fresh mulberry leaves, and artificial diets do not support good health. The aim of this study was to explore the relationship between the dietary transition from artificial diets to mulberry leaves and the effects on the gut microbiota and physiological changes in silkworms as a model organism. With the transition from artificial diets to mulberry leaves, the diversity of the silkworm gut microbiota increased, and the proportion of Enterococcus and Weissella, the dominant gut bacterial species in silkworms reared on artificial diets, decreased, whereas the abundance of Achromobacter and Rhodococcus increased. Dietary transition at different times, including the third or fifth instar larval stages, resulted in significant differences in the growth and development, immune resistance, and silk production capacity of silkworms. These changes might have been associated with the rapid adaptation of the intestinal microbiota of silkworms to dietary transition. This study preliminarily established a dietary transition-gut microbial model in silkworms based on the conversion from artificial diets to mulberry leaves, thus providing an important reference for future studies on the mechanisms through which habitual dietary changes affect host physiology through the gut microbiome.

The Ethylene Response Factor ERF5 Regulates Anthocyanin Biosynthesis in 'Zijin' Mulberry Fruits by Interacting with MYBA and F3H Genes

Ethylene promotes ripening in fruits as well as the biosynthesis of anthocyanins in plants. However, the question of which ethylene response factors (ERFs) interact with the genes along the anthocyanin biosynthesis pathway is yet to be answered. Herein, we conduct an integrated analysis of transcriptomes and metabolome on fruits of two mulberry genotypes ('Zijin', ZJ, and 'Dashi', DS, with high and low anthocyanin abundance, respectively) at different post-flowering stages. In total, 1035 upregulated genes were identified in ZJ and DS, including MYBA in the MBW complex and anthocyanin related genes such as F3H. A KEGG analysis suggested that flavonoid biosynthesis and plant hormone signaling transduction pathways were significantly enriched in the upregulated gene list. In particular, among 103 ERF genes, the expression of ERF5 showed the most positive correlation with the anthocyanin change pattern across both genotypes and in the post-flowering stages, with a Pearson correlation coefficient (PCC) of 0.93. Electrophoresis mobility shift assay (EMSA) and luciferase assay suggested that ERF5 binds to the promoter regions of MYBA and F3H and transcriptionally activates their gene expression. We elucidated a potential mechanism by which ethylene enhances anthocyanin accumulation in mulberry fruits and highlighted the importance of the ERF5 gene in controlling the anthocyanin content in mulberry species. This knowledge could be used for engineering purposes in future mulberry breeding programs.

The differences in cocoon and silk qualities among sex-related mulberry and silkworm feeding groups

Sexual dimorphism is seen in many dioecious plant and animal species, which may influence their trophic interactions. The differences in trophic interactions derived from sexual dimorphism in plants may influence herbivorous performance and population dynamics. Both silkworm (Bombyx mori L.) and mulberry (Morus alba L.) usually exhibit sexual dimorphism. However, few studies have been conducted on the effect of sex-related silkworm and mulberry pairings on cocoon and silk qualities, which are crucial in sericulture. Here, we compared the differences in cocoon and silk qualities under four feeding combinations (FS-FL: female silkworm fed with leaves from female mulberry trees; MS-FL: male silkworm fed with leaves from female mulberry trees; FS-ML: female silkworm fed with leaves from male mulberry trees; MS-ML: male silkworm fed with leaves from male mulberry trees). The results showed that silkworms exhibited male-biased herbivory with more male mulberry leaves digested. The FS-ML group had higher silk weight and silk ratio of fresh cocoons than the FS-FL group, and the MS-ML group had lower coarse points than the MS-FL group. Compared with groups FS-ML and FS-FL, both MS-FL and MS-ML had smaller cocoons with longer silk lengths and a higher silk ratio of the fresh cocoons. In addition, the Entropy Weight-TOPSIS method showed the cocoon quality rank as FS-ML > FS-FL > MS-FL > MS-ML, whereas silk quality rank was MS-ML > FS-FL > FS-ML > MS-FL. These results indicate that the quality of cocoon and silk is related to the interaction of silkworm and mulberry at the sex level. Furthermore, female silkworms fed with female and male tree leaves have a higher total yield in cocoon production, while male silkworms fed with male tree leaves produced higher silk quality.

The gut commensal bacterium Enterococcus faecalis LX10 contributes to defending against Nosema bombycis infection in Bombyx mori

BACKGROUND

Microsporidia, a group of obligate intracellular fungal-related parasites, have been used as efficient biocontrol agents for agriculture and forestry pests due to their host specificity and transovarial transmission. They mainly infect insect pests through the intestinal tract, but the interactions between microsporidia and the gut microbiota of the host have not been well demonstrated.

RESULTS

Based on the microsporidia-Bombyx mori model, we report that the susceptibility of silkworms to exposure to the microsporidium Nosema bombycis was both dose and time dependent. Comparative analyses of the silkworm gut microbiome revealed substantially increased abundance of Enterococcus belonging to Firmicutes after N. bombycis infection. Furthermore, a bacterial strain (LX10) was obtained from the gut of B. mori and identified as Enterococcus faecalis based on 16S rRNA sequence analysis. E. faecalis LX10 reduced the N. bombycis spore germination rate and the infection efficiency in vitro and in vivo, as confirmed by bioassay tests and histopathological analyses. In addition, after simultaneous oral feeding with E. faecalis LX10 and N. bombycis, gene (Akirin, Cecropin A, Mesh, Ssk, DUOX and NOS) expression, hydrogen peroxide and nitric oxide levels, and glutathione S-transferase (GST) activity showed different degrees of recovery and correction compared with those under N. bombycis infection alone. Finally, the enterococcin LX protein was identified from sterile LX10 fermentation liquid based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis.

CONCLUSION

Altogether, the results revealed that E. faecalis LX10 with anti-N. bombycis activity might play an important role in protecting silkworms from microsporidia. Removal of these specific commensal bacteria with antibiotics and utilization of transgenic symbiotic systems may effectively improve the biocontrol value of microsporidia. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Construction and analysis of the protein-protein interaction network for the olfactory system of the silkworm Bombyx mori

Olfaction plays an essential role in feeding and information exchange in insects. Previous studies on the olfaction of silkworms have provided a wealth of information about genes and proteins, yet, most studies have only focused on a single gene or protein related to the insect's olfaction. The aim of the current study is to determine key proteins in the olfactory system of the silkworm, and further understand protein-protein interactions (PPIs) in the olfactory system of Lepidoptera. To achieve this goal, we integrated Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and network analyses. Furthermore, we selected 585 olfactory-related proteins and constructed a (PPI) network for the olfactory system of the silkworm. Network analysis led to the identification of several key proteins, including GSTz1, LOC733095, BGIBMGA002169-TA, BGIBMGA010939-TA, GSTs2, GSTd2, Or-2, and BGIBMGA013255-TA. A comprehensive evaluation of the proteins showed that glutathione S-transferases (GSTs) had the highest ranking. GSTs also had the highest enrichment levels in GO and KEGG. In conclusion, our analysis showed that key nodes in the biological network had a significant impact on the network, and the key proteins identified via network analysis could serve as new research targets to determine their functions in olfaction.

iTRAQ-Based Quantitative Proteomic Analysis of Digestive Juice across the First 48 Hours of the Fifth Instar in Silkworm Larvae

The silkworm is an oligophagous insect for which mulberry leaves are the sole diet. The nutrients needed for vital activities of the egg, pupal, and adult stages, and the proteins formed in the cocoon, are all derived from the larval stages. The silkworm feeds and grows quickly during the larval stages. In particular, the amount of leaf ingested and digested quickly increases from the ecdysis to the gluttonous stage in the fifth instar period. In this study, we used the iTRAQ proteomic technique to identify and analyze silkworm larval digestive juice proteins during this period. A total of 227 proteins were successfully identified. These were primarily serine protease activity, esterase activity, binding, and serine protease inhibitors, which were mainly involved in the digestion and overcoming the detrimental effects of mulberry leaves. Moreover, 30 genes of the identified proteins were expressed specifically in the midgut. Temporal proteomic analysis of digestive juice revealed developmental dynamic features related to molecular mechanisms of the principal functions of digesting, resisting pathogens, and overruling the inhibitory effects of mulberry leaves protease inhibitors (PIs) with a dynamic strategy, although overruling the inhibitory effects has not yet been confirmed by previous study. These findings will help address the potential functions of digestive juice in silkworm larvae.

Isolation of high γ-aminobutyric acid-producing lactic acid bacteria and fermentation in mulberry leaf powders

γ-Amino butyric acid (GABA) has numerous roles in physiological processes, including neurotransmission, and induction of hypotensive, diuretic and tranquilizer effects. The present study aimed to produce GABA-enriched mulberry leaf powder by using a strain of high GABA-producing Lactobacillus pentosus SS6, which is isolated from fermented mulberry fruits. A total of 37 strains of lactic acid bacteria (LAB) were isolated from fermented mulberry fruits strains of high GABA-producing Lactobacillus pentosus were selected. The isolated LAB was analyzed using thin-layer chromatography. SS6 was used as a starter culture for the fermentation of mulberry leaf powder to produce GABA. The mulberry leaf powder was treated with 10% saccharose, 6% peptone, 1.6% K₂HPO₄, 1% L-sodium glutamate at 35°C for 36 h (each treatment was applied whilst the others were kept constant), in a mixture with a water content of 60%, with the respective LAB strain that was fermented by incubation at 30°C for 6 h. The results indicated that the SS6 strain produced significantly higher GABA contents in the fermentation broth compared to the other strains (P<0.05). Addition of 10% saccharose, 6% peptone, 1.6% K₂HPO₄ and 1% L-sodium glutamate significantly triggered the production of GABA compared with that in the groups void of those additives (P<0.05). Furthermore, the water content, treatment time, amount of LAB inoculated and the incubation temperature also significantly affected GABA production compared with untreated groups under the aforementioned conditions (P<0.05). In conclusion, 10% saccharose, 6% peptone, 1.6% K₂HPO₄, 1% L-sodium glutamate, and a 60% water content at 35°C significantly improved and enhanced GABA production. The present study provided a basis for the production of GABA, which may be utilized by the pharmaceutical and food industry.

Organ-Specific Analysis of Morus alba Using a Gel-Free/Label-Free Proteomic Technique

Morus alba is an important medicinal plant that is used to treat human diseases. The leaf, branch, and root of Morus can be applied as antidiabetic, antioxidant, and anti-inflammatory medicines, respectively. To explore the molecular mechanisms underlying the various pharmacological functions within different parts of Morus, organ-specific proteomics were performed. Protein profiles of the Morus leaf, branch, and root were determined using a gel-free/label-free proteomic technique. In the Morus leaf, branch, and root, a total of 492, 414, and 355 proteins were identified, respectively, including 84 common proteins. In leaf, the main function was related to protein degradation, photosynthesis, and redox ascorbate/glutathione metabolism. In branch, the main function was related to protein synthesis/degradation, stress, and redox ascorbate/glutathione metabolism. In root, the main function was related to protein synthesis/degradation, stress, and cell wall. Additionally, organ-specific metabolites and antioxidant activities were analyzed. These results revealed that flavonoids were highly accumulated in Morus root compared with the branch and leaf. Accordingly, two root-specific proteins named chalcone flavanone isomerase and flavonoid 3,5-hydroxylase were accumulated in the flavonoid pathway. Consistent with this finding, the content of the total flavonoids was higher in root compared to those detected in branch and leaf. These results suggest that the flavonoids in Morus root might be responsible for its biological activity and the root is the main part for flavonoid biosynthesis in Morus.

Transcriptome analysis and identification of key genes involved in 1-deoxynojirimycin biosynthesis of mulberry (Morus alba L.)

Mulberry (Morus alba L.) represents one of the most commonly utilized plants in traditional medicine and as a nutritional plant used worldwide. The polyhydroxylated alkaloid 1-deoxynojirimycin (DNJ) is the major bioactive compounds of mulberry in treating diabetes. However, the DNJ content in mulberry is very low. Therefore, identification of key genes involved in DNJ alkaloid biosynthesis will provide a basis for the further analysis of its biosynthetic pathway and ultimately for the realization of synthetic biological production. Here, two cDNA libraries of mulberry leaf samples with different DNJ contents were constructed. Approximately 16 Gb raw RNA-Seq data was generated and de novo assembled into 112,481 transcripts, with an average length of 766 bp and an N50 value of 1,392. Subsequently, all unigenes were annotated based on nine public databases; 11,318 transcripts were found to be significantly differentially regulated. A total of 38 unique candidate genes were identified as being involved in DNJ alkaloid biosynthesis in mulberry, and nine unique genes had significantly different expression. Three key transcripts of DNJ biosynthesis were identified and further characterized using RT-PCR; they were assigned to lysine decarboxylase and primary-amine oxidase genes. Five CYP450 transcripts and two methyltransferase transcripts were significantly associated with DNJ content. Overall, the biosynthetic pathway of DNJ alkaloid was preliminarily speculated.

Mulberry (Morus spp.) has the features to treat as a potential perennial model system

Mulberry (Morus spp.), a commercially exploited tree species as the host of monophagous pest silk worm (Bombyx mori), belongs to the family Moraceae. The domesticated tree has diverse beneficial characters such as traits associated with rapid growth and biomass production, plant insect/microbe interaction, abiotic stress tolerance and the traits associated with nutritional and medicinal values; some of which have been exploited. Draft genome of Morus notabilis has been sequenced and a large volume of transcriptome and genomic resources have been generated. In this review an attempt has been made to examine the options for considering mulberry as another tree model system to study unique traits associated with perennial systems. The diverse traits and features in mulberry suggest that the system can be a "comprehensive trait integrated tree system" quite different from other model tree systems.

Quantitative ¹H-NMR Spectroscopy for Profiling Primary Metabolites in Mulberry Leaves

The primary metabolites in aqueous extract of mulberry (Morus alba L.) leaves were characterized by using proton nuclear magnetic resonance (¹H-NMR) spectroscopy. With the convenience of resonance assignment, GABA together with the other 10 primary metabolites was simultaneously identified and quantified in one ¹H-NMR spectrum. In this study, external calibration curves for metabolites were employed to calculate the concentrations of interests. The proposed quantitative approach was demonstrated with good linearity (r² ranged in the interval of 0.9965–0.9999), precision, repeatability, stability (RSD values in the ranges of 0.35–4.89%, 0.77–7.13% and 0.28–2.33%, respectively) and accuracy (recovery rates from 89.2% to 118.5%). The established ¹H-NMR method was then successfully applied to quantify 11 primary metabolites in mulberry leaves from different geographical regions within a rapid analysis time and a simple sample preparation procedure.